An operator shortage has left scheduled buses sitting still at Muni yards, engines cold. Those “not outs,” Muni operator-slang for a bus or train “not out in service,” have caused drastically long wait times for service across San Francisco for months, public data obtained and analyzed by the San Francisco Examiner shows.

On any particular weekday almost a hundred buses — ones meant to run — sit unused due to a lack of operators. The usual lines for downtown buses have grown into crowds. Lucky riders find themselves packed ever-closer to their fellow passengerswhile unlucky riders see full-to-the-brim buses pass them up outright.

Riders have seen wait times lag on the most crucial commuter lines: 48 minute waits on the 1BX, 24 minute waits on the 38-Geary, 27 minute waits on the 1-California. Major slowdowns have hit all of San Francisco’s neighborhoods, from rich to poor, cutting across all of the diverse populations that rely on Muni for work and school.

John Haley, who heads Muni operations at the San Francisco Municipal Transportation Agency, said the problem started in late March and has only worsened.

“There’s service being missed everywhere,” Haley told the Examiner in mid-July.

A perfect storm of circumstances stressed Muni’s training pipeline this summer, according to transit officials, public documents, and sources in Muni’s ranks. This resulted in an operator shortage SFMTA officials struggled and failed to prevent.

The Twin Peaks Tunnel shutdown required additional buses and more operators to be trained to drive them, while at the same time newly purchased, technologically-advanced light rail vehicles required even more operator training. Further compounding this training backlog, a union-mandated “general sign-up” — which occurs regularly — saw operators flocking to drive new routes within Muni. Some of those new assignments were paused, Haley said.

“It’s what I’d call a pipeline problem,” Haley said.

An internal email obtained by the Examiner show the transit department of SFMTA warned the training department of this potential training backlog in October last year.

That email states operator promotions and retirements also led to attrition. Burned-out Muni drivers angry over contracts that restrict new operators’ pay for five years, a bargaining change negotiated in 2014, have also led to a dearth of operators, according to the Transport Workers Union Local 250-A.

“The operators are trained, the majority are quitting,” said Roger Marenco, president of local TWU Local 250-A. “I was riding a bus with a woman who said she was a part-time operator for four months. Why doesn’t the agency make her full time? What is the agency waiting for?”

The resulting impact to riders is harder to see with the naked eye than, say, a BART tunnel shutdown that leaves riders visibly stranded on train platforms — but the slowdown has rocked the commute of thousands more riders, as Muni’s daily ridership is more than 700,000 trips, nearly double that of BART. Roughly 25 percent of all vehicle trips in San Francisco are on transit.

And, unlike a tunnel shutdown, this Muni slowdown has persisted for months.

The Examiner crunched Muni service data provided by SFMTA for weeks between May and July. An average of daily service data for the week July 2-6, for instance, shows a staggering 8 percent of service hours missed each day. That means Muni service was operating at 92 percent efficiency, 3 percent below city-mandated service levels and 6.5 percent below its optimum service levels.

For instance, the average weekday in early July had 863 hours of service missed on Muni citywide out of a total 9,700 hours of scheduled service. For context, one bus trip along its route can be measured at about an hour, and as a rule of thumb eight hours of service is one bus “run,” according to SFMTA.

Though that may be tough to translate into the real world, think of it this way: It takes a 38-Geary roughly an hour to cross from downtown to Ocean Beach. Eight hours less service is akin to removing one 38 bus shift from the ten 38 bus shifts that traverse The City at any one time, leading to a ripple effect of longer waits and more crowding on those remaining buses.

That problem has only grown.

About ten major Muni routes were missing more than ten hours worth of service daily in late April, according to SFMTA data. But by the week of June 25, more than 30 Muni routes citywide were missing more than ten hours worth of daily service, a trend that continued through July.

The 8-Bayshore, for instance, had an average 80 missed service hours every day in early July out of a total 460 scheduled service hours. The 38-Geary had an average 47 missed service hours for the same time period out of a total 186 scheduled service hours.

Both lines are among Muni’s most heavily trafficked, the backbone of San Francisco transit. That’s by design, Haley said.

Faced with dire bus-service choices without enough operators to drive, Muni has opted to short service on lines that run dozens of buses, because not running buses on routes with fewer buses would have a greater impact on timely service, Haley said.

Data on bus “not outs,” meaning buses not out on the street for service, shared with the Examiner by irate Muni operators, show as many as 199 scheduled Muni on runs not out on one July weekday. Internal SFMTA communications show a deficit of 150 Muni operators late last year, a problem that has only worsened.

Muni riders have jumped on to social media to scorch SFMTA publicly.

“Why no inbound 1BX for 20 minutes? I rely on this to get to work and now I’m late,” wrote Twitter user Maria Grimm on July 24. “Seventh straight week of bus-route service cutbacks that @sfmta_muni refuses to acknowledge or fix,” wrote Twitter user Mike Murphy on July 23, as he tweeted a photo of a 27 minute wait for the 38-Geary. “Are there not enough drivers for the new buses @LondonBreed advocated for?,” wrote Twitter user Ashley Moon on July 25. Moon added that a group of 10-15 people were passed by three different buses that morning, causing them to wait 48 minutes for a bus. Moon added, “I’ve been a loyal Muni rider for years and never experienced so much frustration as I have the last few months.”

To those concerned with the slowdowns, Haley said riders should see some relief by August 25, when the Twin Peaks tunnel reopens and the need for bus operators lessens. And SFMTA said it is adding more training staff, recruiting retired operators, and adjusting shift policies to address the issue.

Still, the operator shortage may then shift to light rail service, Haley said, if needed training is not completed soon.

The number of missed runs, he said, is “not acceptable under any circumstances.”